Porcelain wheels or casters are older than the more common,wood ones. These stout casters date from around 1850 to 1895. ,This set is for a bed. The brackets bolt to the side of the bed and,the stem of the wheel is inserted into the bracket. , ,The bracket mounting plate is 3 1/4″ x 2 1/2″. The bracket projects,out from the bed 3 inches. Each stem of the castors are 3 1/2″ long,but ground out in the bracket at 3 inches. The wheels are 1 7/8″,round and are in very good condition. , ,A set of caster like these will raise the bed by at least 2 1/2 to 3″,,and will allow you to move a large bed easily.